1. Field of the Invention
This invention relates to a network transport system, and more particularly to the transmission of multiple data streams, collectively representative of a client signal, at high rates across a digital optical network infrastructure.
2. Description of the Related Art
Using various optical networking technologies, high capacity transport systems are employed to meet the ever increasing demand of transporting high speed client data across a communication network infrastructure. Certain transport systems have been designed to receive a client signal at a first terminal node or transmit end of the system and re-format the client signal for transmission over the network infrastructure. The re-formatted signal often complies with a transmission standard, such as the Optical Transport Network (hereinafter, “OTN”) protocol or other proprietary formats. At a second terminal node or receive end of the network infrastructure, the client signal is obtained from the re-formatted signal and supplied to the client. then received by the client at a second terminal node.
Some transport systems are designed to interface with various types of client networks. In so doing, the transport system maps data from a client signal into a transport frame in which the data propagates across a transport connection. This mapping procedure is typically specific to the protocol of the client signal and the format of the transport system so that the client signal may be completely reconstructed at a transport receiver terminal. The transport terminal nodes, both transmitter and receiver nodes, are generally able to operate in different modes depending on the type of client signal that is being processed. For example, a transport terminal node may map a client Synchronous Optical Network (“SONET”) frame into a transport frame using a first mapping procedure or an Ethernet frame into a transport frame using a second mapping procedure.
The transmission characteristics of the client data across the transport connection may depend on both the protocol and rate of the particular client signal. To ensure proper backward compatibility with legacy network schemes and to provide for timing necessary to adequately process the client signal during transmission from transmit end to receive end, some transport systems are designed to include data paths which operate at a fraction of the rate at which the client data was provided. Therefore, if a client signal having a data rate of 10 Gbps, for example, is provided to the transport system, the transport system can then process the incoming signal into multiple signals or data streams, for example four signals each at a rate of 2.5 Gbps. By properly selecting this lower rate, such as 2.5 Gbps, a more efficient transport system can be designed, allowing the transport system to accept and process a client signal regardless of the incoming bit rate or protocol of that signal. In this way, the transport system can retain backward compatibility with legacy networking schemes, while supporting future networking schemes employing faster bit rates and newer protocols. Moreover, at a transmitter node for example, such transport systems may recombine a number of the lower rate data streams for transmission on a specific optical wavelength, as part of a wave division multiplexed (hereinafter, “WDM”) signal, across the network infrastructure. Thus, the lower data rate streams can be a fraction of the data capacity per wavelength, as well.
In order to ensure that the client signal is properly recombined at the receiver terminal node, great care must be taken. In some transport systems a client signal is transported across the network infrastructure on a per lambda basis. That is, any given client signal is transported across the network infrastructure, or portion thereof, on a single wavelength, as part of a WDM signal. In this way, the transport system can track the progress of the signal and ensure its proper delivery and processing at a corresponding receiver terminal node.
In such systems, however, the full capacity of the optical carrier may not be fully utilized. For example, in transport systems utilizing 10 Gbps per wavelength transmission systems, if a client signal is received at a rate of 2.5 Gbps, 7.5 Gbps of bandwidth of the transmission system related to that particular wavelength would not be utilized. Additionally, there may another client signal which has a data rate of 7.5 Gbps and, thus, resulting in the underutilization of 2.5 Gbps of bandwidth.
Some transport systems provide for a constant or fixed data rate across the network infrastructure, such as from a transmitter terminal node where a client signal is transmitted to a receiver terminal node where the client signal is provided back to the client. In this way, all the packets or frames which make up the client signal are fixed with respect to size and data rate and, thus, are more easily handled during its transport across the network infrastructure, allowing for a more simple transport system solution since the hardware and software which forms the network infrastructure need only be concerned with the handling of a single type of transport frame. In such systems various smaller transport frames can be combined to form larger transport frames to meet the requirements of the optical transport subsystem. For example, if the digital optical network communicates 10 Gbps per lambda, e.g. per wavelength, then various transport frames of lower rates can be combined until the maximum rate is achieved, such that a larger frame is created which has a data rate substantially equal to 10 Gbps. For purposes herein, these smaller transport frames are referred to as intra-nodal frames since they represent client signal data at a node element as part of the network infrastructure, at a terminal node for example, while the larger transport frames are referred to as line side frames since these frames are utilized for the transmission of data from intermediate node to intermediate node across the network infrastructure.
As the client signal propagates across the network infrastructure within a line side frame format structure, from a transmitter terminal node, through multiple intermediate nodes, and finally reaching a desired receiver terminal node, the client signal may be reconditioned along the way, such as through various electrical or optical signal processing including, but not limited to, FEC encoding, decoding and re-encoding, in addition to signal amplification, signal reshaping and signal retiming, or otherwise regeneration or reconstruction of the signal, typically referred to as “3R” processing. All such processing is performed on the data in the form of intra-nodal frame format structures. Furthermore, although not specifically necessary for carrying out the present invention, some transport systems can freely accept various client signals or varying data rates. Such as those disclosed in, for example, U.S. patent application Ser. No. 11/154,455, entitled “UNIVERSAL DIGITAL FRAMER ARCHITECTURE FOR TRANSPORT OF CLIENT SIGNALS OF ANY CLIENT PAYLOAD AND FORMAT TYPE,” which is incorporated in its entirety herein by reference.
What is needed is a transport system which allows for transmission of a client signal across a network infrastructure without the need to transmit the client signal, or the various intra-nodal frames representative of the client signal, on the same wavelength over each optical span of a network infrastructure. Such as a system which is configurable to allow for spreading, or otherwise redirecting, various portions of the various client signals to fully utilize the bandwidth available by the transport system, realigning the data streams at the receiver terminal node and then recapturing the original client signals. Furthermore, what is needed is a transport system which can rearrange and combine various intra-nodal frames into desired line side frames to provide for efficient transmission of client data across the network infrastructure.
Further, what is needed is a transport system which is configurable to allow for selectively generating such desirable line side frames, comprising intra-nodal frames of more than one client signal for example, while taking into account the various problems associated with transmission of such client signals spanning multiple wavelengths, such as skew between or across the various intra-nodal frames representative of a client signal, as it travels from one intermediate node to another across the network infrastructure. Last, what is needed is a transports system which fulfills one or more of the above needs regardless of the format of the client signal as provided by the client for deployment on the network infrastructure.